1. Field of the Invention
This invention concerns a product for abstracting dissolved ions from aqueous solutions, and more particularly concerns an open-celled cellulosic sponge which non-occlusively holds an ion-selective polymer.
2. Description of the Prior Art
U.S. patent application Ser. No. 395,535 filed Aug. 18, 1989 now U.S. Pat. No. 5,002,984 discloses a sponge product for absorbing ionic species from aqueous solutions. The product is made from an open-celled sponge of regenerated cellulose which is caused to hold a large quantity of isolubilized polyethyleneimine (PEI) in a manner which does not significantly occlude the pores of the sponge. The insolubilized PEI, having selective ion absorption characteristics, has a water-swelling characteristic similar to that of the cellulose, thereby enabling it to remain attached to the water-swollen sponge.
However, if the sponge product is re-cycled between dry and wet states, the insolubilized PEI will gradually separate from the sponge. For this reason, it is best to maintain the sponge in water-swollen form. The wet or water-swollen form is in fact the initially produced form of the sponge product, the reason being that a water wash step is utilized to cleanse the sponge of any unreacted PEI and other interactive species.
In view of the use of certain polyfunctional carboxylic acids for achieving the insolubilization of the PEI, and some oxidation of cellulose which occurs during a thermal curing step which effects said insolubilization, the resultant sponge product is generally found to have a pH below 5.0.
When stored wet in sealed containers for prolonged periods of time, it has been found that the sponge product, at pH values below 5.0, undergoes microbial degradation. The degradation, which adversely affects the performance of the product becomes visible as regions of black, white, brown or green discoloration indicative of the effects of mold, mildew and fungus. Attempts to alleviate this problem with conventional anti-microbial agents have been tried unsuccessfully. One of the difficulties in overcoming this problem is that the product, usually in the form of cubes of about 1/2" size, has a high surface area for microbial attack, and the considerable space between adjacent sponges in bulk packaging permits facile cross-contamination of adjacent sponges.
It is accordingly an object of the present invention to provide a wet cellulosic sponge product containing insolubilized PEI and having resistance to microbial degradation.
It is another object of this invention to provide a sponge product of the aforesaid nature wherein said insolubilized PEI has water-swelling characteristics similar to that of cellulosic sponge.
It is a further object of the present invention to provide a sponge product of the aforesaid nature of relatively small size, and a commercial package comprising a multitude of said wet sponges confined within a sealed container.
These objects and other objects and advantages of the invention will be apparent from the following description.